A trailer hub carries the wheel, the bearings and often the brake drum. Order the wrong one and either it won’t fit the spindle or the wheel won’t bolt up. Matching a hub comes down to a handful of details you can check in the driveway.
What makes one hub different from another
The number of studs and the bolt circle
The bearings and spindle it’s built for
The hub type: idler, drum or disc
The stud size, which has to match your lug nuts
The capacity it’s rated for
Step 1: Count the studs
Most trailer hubs have 4, 5, 6 or 8 studs. The count narrows things down quickly, because each one tends to go with a range of axle capacities.
Studs | Common bolt circle | Typical use |
|---|---|---|
4 | 4″ | Light utility trailers |
5 | 4-1/2″ | Trailers up to 3,500 lb per axle |
6 | 5-1/2″ | 5,200–6,000 lb axles |
8 | 6-1/2″ | 7,000 lb axles and up |
Good to know
These are the most common pairings, not guarantees. 5 on 4-1/2″ and 5 on 4-3/4″ are easy to mix up, so measure even if the table looks like a match.
Step 2: Measure the bolt circle
The bolt circle is the diameter of the circle that runs through the center of the studs. How you measure it depends on whether you have an even or odd number of studs.
4, 6 or 8 studs
Measure from the center of one stud to the center of the stud directly across from it.
5 studs
There’s no stud directly across, so measure from the back edge of one stud to the center of the third stud, skipping the one in between. It’s an easy measurement to get wrong, so bring a wheel or the old hub in if you’re unsure.
Step 3: Identify the hub type
Idler hub: no brake, just the hub and bearings. Common on smaller trailers and on the non-braked axle of a tandem.
Drum hub: the hub and brake drum are one piece. Used with electric or hydraulic drum brakes.
Disc hub: the hub carries a brake rotor, either built in or bolted on. Common on boat trailers with hydraulic disc brakes.
The hub type has to match the brakes on that wheel. A drum hub won’t work with a disc caliper, and an idler hub can’t be used where there’s a brake.
Step 4: Match the bearings and spindle
The bearing races pressed into the hub have to suit the spindle on your axle. Read the numbers stamped on your bearings; our guide on how to identify wheel bearings shows where to find them. A common 3,500 lb setup uses L68149 inner and L44649 outer bearings, while many 5,200–7,000 lb axles use 25580 inner and 15123 outer.
Step 5: Check the studs and grease system
Note the stud thread size, because your lug nuts and wheels have to match it. Also look at the end of the spindle: if there’s a grease fitting, you have a self-lubricating spindle, and you’ll want a dust cap with a rubber plug so you can keep using it.
Hub kits vs bare hubs
Many hubs are sold as kits with bearings, races, a seal, a dust cap and lug nuts in the box. Replacing the hub as a kit is usually simpler and safer than reusing old bearings. Replace both hubs on an axle at the same time so the trailer brakes and rolls evenly.
What to bring to the store
Stud count and bolt circle
Hub type: idler, drum or disc
Bearing numbers, or the old bearings in a bag
Axle capacity from the tag
A photo of the hub face and the end of the spindle
Get the part or the repair
Shop online for local pickup, or bring the old part to our Port St. Lucie store at 496 SW Voltair Terrace and we’ll help you match it. Not comfortable doing the job yourself? Request a repair and we’ll take care of it, or call us on 772-924-7299.
Guides are general advice. Trailers vary, so check your trailer’s labels and manuals, or ask us before you order.
